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exd lib exd query_runner where.ex
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lib/exd/query_runner/where.ex 

defmodule Exd.Runner.Where do

  @moduledoc """

  Where clause

  """

  alias Exd.Resolvable

  alias Exd.Record



  @type resolvable :: binary()

  @type relation :: :> | :< | := | :<>

  @type value :: any()



  @doc """

  Resolves select statement

  """

  @spec where(Flow.t(), resolvable(), relation(), value()) :: Flow.t()

  def where(flow, field, relation, value) do

    flow

    |> Flow.map(&mark_as_filtered(&1, field, relation, value))

    |> Flow.reject(&Record.flag?(&1, :filtered))

  end



  defp mark_as_filtered(record, field, relation, value) do

    if match?(record, field, relation, value) do

      record

    else

      Record.flag(record, :filtered)

    end

  end



  defp match?(record, field, relation, value) do

    left = Resolvable.resolve(field, record)

    right = Resolvable.resolve(value, record)

    do_match?(relation, left, right)

  end

  defp do_match?(:>, left, right), do: left > right

  defp do_match?(:<, left, right), do: left < right

  defp do_match?(:=, left, right), do: left = right

  defp do_match?(:<>, left, right), do: left != right



end